Survival of Rhizobium trifolii on white clover seed before sowing is adversely affected by both drying and a water-soluble toxin which di f fuses f rom the seed coat dur ing the inocula t ion process . Survival of rhizobia is increased by removal of the toxin by seed washing or the suppress ion of i t s inhib i tory ef fec t by t rea tment of seed wi th phenol ic adsorbents . Surv iva l o f rh ...

Congo red absorption is generally considered a contraindication of Rhizobium. However, R. leguminosarum takes up the dye on yeast extract-mannitol agar. The uptake of congo red varies among strains of R. leguminosarum, as shown elsewhere with strains of R. trifolii and R. meliloti. Congo red absorption does not distinguish rhizobia from other bacteria, but may be useful as a strain marker.

Mutant strains of Rhizobium trifolii that induce nitrogenase activity in the free-living state were isolated. These strains, unlike the wild type, nodulated soybean and mungbean plants, producing effective nodules. One of the strains, strain DT72, also nodulated clover but the nodules were ineffective. Strain DT125 consumed hydrogen gas from the gas phase, which can be coupled to nitrogenase ac...

Of 18 Rhizobium trifolii strains tested, 12 showed a high frequency of loss of nodulation ability after incubation in cultures at elevated temperatures. A correlation between loss of nodulation ability and loss of a large plasmid was demonstrated for R. trifolii. In some nonnodulating (Nod-) mutants, deletions occurred instead of total elimination of the plasmid molecule. The maximum curing eff...

The symbiotic plasmid (pSym) of Rhizobium leguminosarum bv. trifolii 4S5, which carries Tn5-mob, was successfully transferred into Agrobacterium tumefaciens A136 by using a conjugation method. The resulting transconjugants induced the development of ineffective nitrogen-fixing nodules on the roots of white clover seedlings. Depending on the manner in which the pSym was retained, the transconjug...